1. Field of the Invention
The present invention relates to a stacked piezoelectric device used for a piezoelectric actuator and the like.
2. Description of the Related Art
A piezoelectric device composed of a piezoelectric material, such as a piezoelectric ceramic, is characterized by generating a force or displacement when a voltage is applied, and generating a voltage when a force is applied, and it has a wide range of application such as various actuators and sensors. A stacked piezoelectric device, which is a concept including a stacked piezoelectric actuator, comprising a plurality of piezoelectric layers composed of piezoelectric material, is often used in order to obtain large generated force or displacement, in particular, when it is used for an actuator and the like.
A common stacked piezoelectric device is fabricated by stacking piezoelectric material layers and internal electrode layers alternately, and then calcining the resulting stack in one body. A metal paste used as electrode material comprises a powder of noble metal, such as Ag—Pd, and a binder. As an internal electrode material, a metal paste further blended with a piezoelectric material component or an analogue thereof is used in order to prevent delamination (interlaminar peeling) due to the calcining shrinkage difference between a piezoelectric material and an internal electrode. See, for example, Japanese Unexamined Patent Publication No. 57-30308.
However, in this case, there has been a problem that crystals of the piezoelectric material, which are insulating material, deposit in the internal electrode layer after calcination, and pores essentially tend to occur because a metal paste contains a binder and, therefore, the conductive material in the internal electrode layer is not continuous, and the electric transmission efficiency from an internal electrode to a piezoelectric layer is lowered.
There has been also a problem that an internal electrode material containing noble metals, such as Ag—Pd, is expensive. Therefore, there is also an idea that Cu can be used as an internal electrode material in order to cut the cost. In this case, there is a problem that, as Cu is easier to oxidize than a noble metal, such as Ag—Pd, oxidation of Cu advances, with pores in the internal electrode layer and in the interface between a piezoelectric material layer and an internal electrode layer as the starting points, while in use and Cu oxide is produced and, thereby, the electric transmission efficiency further declines and delamination is caused due to a reduction in the strength of an electrode layer.